Power issue 03 5.4

[Fanatic1074]

I just lose a lot of power. It feels like the truck barely wants to pull its own weight. But it doesn't seem to be missing at all. I don't think the emissions leak is in the throttle body though I'm pretty sure the emissions leak is in the tank. The reason I say this is because about 4 years ago I had a emissions leak and it was in the tank as well. At the time the leak was around for where the fuel pump mounts. It seems that the tank was warping. I put a new seal and some dielectric grease in there and it stopped the leak. My guess is that has come back. It also makes sense because it has been getting worse and worse over the last couple of years. And maybe that leak was small and now it's getting larger and larger. I just am not sure if emissions leak would cause the issue that I am experiencing.

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[joezek]

My last expedition had an intermittent emission system leak/check engine light. I changed the fuel cap and that fixed the problem.

I just bought an old BMW recently, one problem it had was weak power. I was told the filter was "New". I looked at it, and found they had the filter installed backwards and it was restricting flow. Just something to think about, maybe its in backwards and clogged up very quickly.

If it's intermittent, could be a loose connector on a sensor like TPS or something. But you'd probably get a failed sensor check engine light. I still keep thinking fuel pump or fuel pump regulator. What year is it?

 

[Fanatic1074]

2003. And there is a new cap on it and its a k&n cai that I just cleaned. Its can't be installed backwards.

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[joezek]

Any new news, is it fixed yet?

 

[Fanatic1074]

Nope. Just ordered a high flow MAF. Figured maybe the stock one can't keep up with the extra flow and causing me to run lean. I'll let u now the results.

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[Darkhorse393]

I'm a noob here but could the problem be in the transmission? If the torque convertor is locking up at the wrong time it could stall under braking or if its not down shifting properly that would give a low power feeling when trying to accelerate. just firing out ideas since you seem to have done everything engine related

 

[Fanatic1074]

Possibly. I don't know a whole lot about transmissions. I have had a pressure flush done. It was around 125k. The tech said it was way cleaner than he expected. No chunks or shards in the pan and the magnet was clean. Tech said that if the torque converter was bad there would be carbon like shavings in it and he said there weren't.

Does that sound OK??? What should I do to test it?

Ohh and occasionally I do feel a slight drop in engine rpm when braking. And there has been a couple of times where I was parked. Put the truck into reverse and the engine ran really rough until I either hit the gas or put it into another gear.

And one last thing. Something when I'm on the interstate and have a lot of stuff in the truck or am pulling a load and the truck needs to downshift to get up a hill it something it seems a little rough when it shifts.

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[BIG AL D]

I did not read all of the posts but my 03 was doing this and I to had COP issues so I thought that is what it was. I was at the Auto Zone going to get the part and they guy said let me read the codes to make sure. He did and it turned out I had a ole in a vacuum hose under all of the plastic. Once I replaced the hose, 2.14, and erased the code my 03 was running better then it had in a long time.

 

[Fanatic1074]

What vacuum hose? I know u said under all the plastic but im not sure what you are referring to. Thanks!

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[BIG AL D]

Not sure, the hose was only about 8 inches long and connected to a part with a sensor in it. I was also getting really bad mileage and it helped thst out also.

 

[buildingdoc]

Probably referring to the vacuum line that runs from the back of the throttle body to the PCV valve. Very common and would reduce throttle response, bad idle, and throw codes. I am battling my own idle issues via an intake vibration/humming as well erratic idle after changing my IAC twice this week. But I did replace that vacuum line and it stopped stalling at lights and crumbled in my hands when removing it.

wish I could be more help as you seem to have replaced everything involving the intake and various sensors, and hope I don't have to go that far.